This invention relates generally to bicycles and particularly to those having multiple sprocket chain drive systems used in off-road or mountain biking.
The sport of cycling has proven to be an extremely popular and long lasting sport and recreational activity. Through the years, a variety of cycling or biking activities have been pursued by a wide range of participants. Not surprisingly, participants in the various cycling or biking activities and recreations have been operative in a variety of environmental circumstances ranging from high speed competition to slow and casual pleasure riding or cycling. In recent years an interesting type of cycling has emerged which is generally referred to as off-road biking or mountain biking. In this sport activity, participants often ride over extremely rough terrain and challenging hill and mountain trails. This activity subjects the bicycle and its operative apparatus to extremes in stress, loading and impact. To meet the need for bicycles capable of operating in such high stress and high load environments over such challenging terrain, practitioner""s in the art have endeavored to provide bicycles which are extremely strong and durable. A competing interest in the production of such strong and durable bicycles is the concurrent need to maintain a substantially light-weight bicycle in order to reduce the energy required to pedal such bicycles across the often hilly and challenging terrain. Toward this end, the typical off-road bicycle utilizes an extremely light-weight frame often fabricated from light-weight exotic metals such as titanium, aluminum and magnesium as well as various high strength alloys thereof. To improve the impact or shock absorption characteristic required to assure sufficient durability and strength of such off-road bicycles, the frame is often fabricated of a plurality of frame portions coupled together using a variety of spring loaded and shock absorbing suspension components. The objective is to provide a frame capable of absorbing substantial impact shock while reducing the energy imparted to the frame through multiply articulated shock absorbing suspension components. The overall objective is to of coarse to avoid damage to the light-weight high-strength frame.
Most off-road bicycles utilize chain drive apparatus in which a plurality of varying diameter sprockets are grouped at the rear wheel and are driven by a pedal crank and chain sprocket drive mechanism. A variety of gear ratios or drive ratios are obtained by the use of a chain derailleur mechanism which is operative to transfer the power coupling chain between the various drive sprockets. In this way, the overall drive ration between the crank and the rear wheel may be varied to allow the user to address different terrain conditions.
While the multiple sprocket train drive systems in use have been refined to provide extremely effective operation and a wide range of drive ratios to a aid the cyclist introverting challenging hills and trails, a problem often arises due to the combined effect of the flexing shock-absorbing frame and the chain drive system. This problem is known generally as xe2x80x9cchain-whippingxe2x80x9d and arises as the articulated frame portions flex to absorb impact and as the loading upon the chain drive is varied in different circumstances. The end result is the creation of undesired slack within the drive chain allowing the upper and lower spans of the drive chain to whip up and down and disengage from the front drive sprocket. Drive chain whipping action is more severe in the upper span of the drive chain (the portion between the rear sprocket and the upper edge of the chain ring) than in the lower span of the drive chain (the portion between the rear sprocket and the lower edge of the chain ring). This results from the tendency of the derailleur mechanism to maintain greater tension in the lower span.
Drive chain engagement can be extremely vexing to a cyclist and under competitive conditions can cause the cyclist to loose his or her ability to effectively compete. Typically, once the drive chain has disengaged from the front sprocket, the cyclist is required to stop and reset the chain upon the sprockets before continuing. In addition, the sudden release of resisting load caused by the chain skipping from the drive socket also creates the possibility of injury to the rider.
In attempting to address the problems associated with disengagement of the drive chain from the front drive sprocket, practitioner""s have attempted to provide bicycle chain drives such as that set forth in U.S. Pat. No. 5,460,576 issued to Barnett which sets forth a BICYCLE CHAIN GUIDE secured to the front hub portion of an otherwise conventional bicycle having a multiple speed chain drive and plural front sprocket coupled to a pedal crank. The bicycle chain guide is pivotally secured beneath the front hub and defines a plurality of staggered step portions corresponding generally to the outer diameters of the plural front sprockets. Sufficient clearance is provided between the step portions and the front sprockets to avoid rubbing against the chain engaged with one of the sprockets. In the event a chain-whipping motion or wave is imparted to the bicycle chain, the step portions of the chain guide captivate the chain against the engaged sprocket to prevent separation thereof.
There arises therefore, a continuing need in the art for evermore improved chain drive systems for bicycles. In particular, there arises a continuing need in the art for systems and apparatus which minimize the effect of chain-whipping in bicycles used under off-road or mountain biking conditions.
Accordingly, it is a general object of the present invention to provide an improved chain drive system for bicycles. It is a more particular object of the present invention to provide an improved chain drive system for bicycles in which the problems of chain-whipping at the front drive sprocket are substantial reduced or eliminated.
In accordance with the present invention there is provided a chain guide apparatus for use in combination with a bicycle drive system having a pedal crank, a chain ring rotated thereby, a frame supporting the pedal crank and a drive chain engaging the chain ring, the chain guide apparatus comprising: a guide support plate and means for supporting the guide support plate upon a bicycle frame and pedal crank; an upper guide block supported by the guide support plate and having a first guide channel formed therein for receiving a bicycle drive chain; and a lower guide block supported by the guide support plate and a second guide channel formed therein for receiving a bicycle drive chain, the upper guide block guiding the bicycle drive chain toward the bicycle chain ring and the lower guide block guiding the bicycle drive chain away from the bicycle chain ring, the upper and lower guide blocks maintaining drive chain engagement despite chain-whipping forces.